Latent prints are invisible fingerprint impressions left on solid surfaces following surface contact caused by the perspiration on the ridges of an individual's skin on their fingers coming in contact with a surface and leaving perspiration behind, making an invisible impression on it. Perspiration is known to contain water, salt, amino acids, and oils, which allows impressions to be made. The natural oils of the body preserve the fingerprint, which is utterly distinct so that no two humans have the same fingerprints.
Conventional methods for extracting fingerprints usually involve adding chemicals or powders to the print. Such conventional methods can present an immediate dilemma in that they force the investigator to make a decision as to whether to dust for prints versus swabbing for DNA evidence.
Automatic non-contact latent fingerprint detection systems are also known that avoid the need to add chemicals or powders that can disturb the surface chemicals of the fingerprint. Such systems generally include a single light source, utilize only diffuse reflectance (reject specular reflection (glare)), and are generally limited to fingerprinting the area of one's finger, or an area about that size.